Change environment variables scope

[mmiranda]

Define the environment variables in the SubCommand process only and not on the global OS scope.

It avoids any kind of misbehaving due to concurrency using the same variable. Ie. HTTPS_PROXY

[codecov-commenter]

Codecov Report

Merging #7 (fcf9b23) into main (900a03a) will increase coverage by 1.77%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##             main       #7      +/-   ##
==========================================
+ Coverage   75.60%   77.38%   +1.77%     
==========================================
  Files           1        1              
  Lines          82       84       +2     
==========================================
+ Hits           62       65       +3     
+ Misses         16       15       -1     
  Partials        4        4              

Impacted Files	Coverage Δ
cfdtunnel/cfdtunnel.go	77.38% <88.88%> (+1.77%)	⬆️

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